Field experiments were conducted for five seasons, 1980/81 through 1984/85, to evaluate the performance and yielding stability of four high-yielding varieties of wheat. Two durum (Crane'S and Bit-tern'S) and two bread wheat (HD 2172 and CM 8237) varieties were grown at Deirab, near Riyadh where high temperatures prevailing at the end of the growing season had very critical effects on the wheat plant. The recommended Yecora rojo was also included as a check variety. Grain yield, yield attributes filling period and filling rate were investigated. Results indicated that seasons significantly affected all traits and the interaction between seasons and varieties was also significant. Grain yield and other traits in the 1982/83 season were superior to other sea-sons and this might be attributed to the cooler temperatures. Regression analysis showed that varieties No. 1, 2 and 3 were stable, whereas varieties No. 4 and 5<br>were unstable, with regard to grain yield production across seasons. The high grain yield was associated with long grain filling period and high rate of grain filling and high kernel weight.